1. Field of the Invention
The present invention relates to a non-contact type tonometer for measuring intraocular pressure of an examinee's eye by blowing compressed air (fluid) to deform a cornea of the eye and detecting a deformed state thereof.
2. Description of Related Art
Intraocular pressure changes with time in synchronization with pulsation (pulse wave) of blood. When the intraocular pressure is measured at random in time by a non-contact type tonometer, it is uncertain which point in variations in intraocular pressure is being measured. For example, if the number of times that measurement is executed is small, the lowest value in the variations in intraocular pressure may be measured even though the actual intraocular pressure is high. In the case of screening such as a mass examination, intraocular hypertension may be overlooked. For this reason, there has been proposed a non-contact type tonometer which measures intraocular pressure in the timing synchronized with a predetermined phase point (position) in pulsation while detecting the pulsation.
As to which value in the variations in intraocular pressure is measured, in general, it depends on purposes of diagnosis, etc. When a contact-applanation-type tonometer is used for making evaluations of measurement results, it requires an average value of measurement results obtained at plural different points in the pulsation phase in addition to a measurement result at an arbitrary point in the pulsation phase. The conventional non-contact type tonometer, however, could provide only the measurement result corresponding to the arbitrary point in the pulsation phase.
It is said that such detection of the pulsation is preferably executed with respect to the forehead of an examinee because the pulsation in the forehead has the periods close to the periods of the intraocular pressure variations. When the pulsation is detected in the forehead, however, there may occur changes due to blinking or otter reasons and reflective movements of the examinee's body by air blow. This results in difficulty in accurately detecting the pulsations Moreover, there are some examinees whose pulse rate and blood pressure change as the measurement is started. This makes it more difficult to perform measurement of accurate intraocular pressure.